The present invention relates to digital computer systems, and more particularly to circuitry for monitoring power supply voltages for a computer system or the like.
Electronic equipment such as a desktop computer has a power supply which receives line current at 110 or 220 V. AC and produces a number of DC supply voltages for powering the integrated circuits, disk drives, and the like. In order to prevent damage or improper operation of the equipment when there is a fault in the power supply, monitor circuits have been used to detect these various voltages and to shut down the equipment when critical supply voltages are outside acceptable ranges of operation. For example, undervoltage and/or overvoltage detectors are used to monitor the +5 V and +12 V supply voltages, as well as negative supply voltages, commonly used to power the microprocessor and memory chips in a desktop computer, and to shut off the operation of the computer when the voltages are out of range. Upon power-up, erratic operation would occur if the initialization routine were started by the CPU before the supply voltages to the chips reached the specified values, and errors could result.
Power supply monitor or supervisor circuits have been previously available for computer systems or the like in which supply voltages are monitored and fault conditions are used to shut down the power supply, and the reset function of the CPU inhibited to prevent premature beginning of the initialization at power-up. However, these prior devices were not able to distinguish anomalous conditions during power-up and power-down in order to prevent erratic operation.
It is a principal object of the invention to provide an improved power supply monitor for a computer or the like, particularly a monitor which provides improved performance during power-up sequences. Another object is to provide an improved method for operating a computer or the like during power-up, particularly by monitoring the power supply voltages to prevent the computer from beginning its initialization routines until the supply voltages are at proper levels, but yet responding to overvoltage or overcurrent to shut off the power supply if faults occur.